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cellular telephone or cellular radio, telecommunications system in which a portable or mobile radio transmitter and receiver, or "telephone," is linked via microwave radio frequencies to base transmitter and receiver stations that connect the user to a conventional telephone network. The geographic region served by a cellular system is subdivided into areas called cells. Each cell has a central base station and two sets of assigned transmission frequencies; one set is used by the base station, and the other by mobile telephones. To prevent radio interference, each cell uses frequencies different from those used by its surrounding cells, but cells sufficiently distant from each other can use the same frequencies. When a mobile telephone leaves one cell and enters another, the telephone call is transferred from one base station and set of transmission frequencies to the next using a computerized switching system. The first cellular telephone system began operation in Tokyo in 1979, and the first U.S. system began operation in 1983 in Chicago. In many countries with inadequate wire-based telephone networks, cellular telephone systems have provided a means of more quickly establishing a national telecommunications network.
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